The busy season begins for Mumbai’s meteorological department. See how they keep an eye on the weather and why they’re not as far off the mark as you think

The clouds are gathering. Sky shots are showing up on Instagram. Umbrella stores in Lohar Chawl and Pydhonie are dusting their display shelves and everyone’s looking up with hope.

An approaching monsoon means most Mumbaikars will roll up their trousers. One team, however, rolls up its sleeves. The 40-member team of scientists, meteorologists and assistants at Colaba’s Regional Meteorological Centre of India Meteorological Department (IMD) is ready for lashings of rain and public curses.

“It’s easily the busiest time of the year,” says Bishwambhar S, chief public relations officer at the centre, which covers the region from Gujarat to Goa. “Everyone takes extra care with their observations and recordings. We have to be a little more careful with our tasks in case of a flood.”

So while year-round record-taking continues day and night – surface readings every three hours, balloon-led upper-air observations in keeping with global practices – the wet season has additional tasks. “We analyse those readings closely for changes in air pressure and the rates of change, and we have models that use temperature, pressure, satellite imagery and wind data to make forecasts so you can prepare for what’s coming.”

A thermograph records weather changes every minute across a 24-hour period.

In addition a pulse-Doppler radar, installed on an 18-storey building in Navy Nagar, offers 3D data about distant objects (even clouds and winds) round the clock. “It’s a very good tool for heavy-rain warnings between Colaba and Santacruz, where the other regional office is located.”

It doesn’t always go as planned. Most city folk would say the IMD’s predictions rarely check out – news of an impending thunderstorm comes too late, promised light showers never materialise, and flood warnings seem redundant when the city has been soaking for hours.

“Our predictions are 95% accurate,” Bishwambhar insists. He believes the problem lies in medium, not message. While their terminology and standard operating procedures work well for hurricane warnings and quakes, they fail in a city where rainshowers last days and even a little rain can wreak havoc. “When we predict the possibility of light rain at one or two spots in Mumbai, and you’re not in the neighbourhoods where rain falls, people think we’ve got it wrong,” he says.

Bishwambhar S marks pressure changes with a pencil.

This monsoon, the forecast is good. “We expect rainfall to be normal between June and September,” Bishwambhar says. “And the rains are expected four days early.”